1. Field of the Invention
The present invention relates to a controller of an internal combustion engine, and more specifically to the control that is implemented when fuel cut is finished to restart fuel supply in an internal combustion engine.
2. Description of the Related Art
In recent years, it is widely known to stop fuel supply to each cylinder of an internal combustion engine, that is, to perform so-called fuel cut, at the time of deceleration or the like of a vehicle. During fuel cut, combustion is not produced in engine cylinders, and the fresh air sucked in by the engine flows directly through an exhaust passage into an exhaust gas purification catalyst. Therefore, a large quantity of oxygen is adsorbed on the exhaust gas purification catalyst.
By the time the engine returns from a fuel cut condition to a fuel supply condition, the exhaust gas purification performance is degraded due to the adsorption of a large quantity of oxygen on the exhaust gas purification catalyst. This causes the problem that the discharge amount of NOx (nitrogen oxides) into the atmosphere is increased. There generates another problem that, shortly after reversion from fuel cut, the brake horsepower of the engine is suddenly changed to cause shock.
In respect of the former problem, there has been developed the technology of early consuming the oxygen adsorbed on the exhaust gas purification catalyst by increasing compensation amount of a fuel injection amount to set an exhaust gas air-fuel ratio to the vicinity of a stoichiometric air-fuel ratio in the time period from the reversion from fuel cut to the implementation of air-fuel ratio feedback control. This technology is disclosed, for example, in Unexamined Japanese Patent Application Publication No. 2003-254126 (hereinafter, referred to as Patent Document 1).
As to the latter problem, there has been developed the technology of preventing shock by reducing an intake air amount and retarding the ignition timing at the time of reversion from fuel cut. This technology is disclosed, for example, in Unexamined Japanese Patent Application Publication No. 6-288327 (hereinafter, referred to as Patent Document 2).
The technology disclosed in Patent Document 1, however, has not been developed in consideration of the shock that is caused along with the reversion from fuel cut.
According to the technology disclosed in Patent Document 2, the misfire limit of ignition timing retardation in normal control of the internal combustion engine is at around zero degree BTDC. For this reason, even if the ignition timing is retarded to the misfire limit, it is hard to reduce the shock sufficiently. In addition, there are problems including one that, since the oxygen adsorption on the exhaust gas purification catalyst during fuel cut is not taken into account, the discharge amount of NOx into the atmosphere is increased, which is an undesirable condition.